Siloxane bischloroformates

ABSTRACT

Siloxane bischloroformates are prepared in a continuous process by phosgenating siloxane bisphenols in a flow reactor using a substantial excess of phosgene and sodium hydroxide. While very high levels (&gt;95%) of conversion of the siloxane bisphenol to the corresponding siloxane bischloroformate are achieved using a flow reactor according to the method of the invention, only more modest conversion (˜90%) of the siloxane bisphenol to the corresponding siloxane bischloroformate is attained when analogous batch processes are employed. The process holds promise for use in the manufacture of silicone-containing copolycarbonates which requires high purity siloxane bischloroformate intermediates.

This application is a division of application Ser. No. 10/223,030, filedAug. 16, 2002 now U.S.Pat. No. 6,723,864, which is hereby incorporatedby reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a method for the preparation ofsiloxane-containing bischloroformates. More particularly the methodrelates to a continuous method for the preparation ofsiloxane-containing bischloroformates in a flow reactor.

Silicone-containing copolycarbonates-are prized for their uniquecombination of ductility, toughness, and flame retardancy. Siliconecopolycarbonates are typically prepared by reaction of a mixture of asiloxane-containing bisphenol and a bisphenol such as bisphenol A underinterfacial conditions with phosgene and an aqueous acid acceptor suchas sodium hydroxide in water. Alternatively, silicone copolycarbonatesmay be prepared by reaction of a chloroformate-terminated polycarbonateoligomer with a siloxane-containing bisphenol. Typically, the reactionbetween the chloroformate-terminated polycarbonate oligomer and thesiloxane-containing bisphenol is carried out under interfacialconditions similar to those employed when a bisphenol and asiloxane-containing bisphenol are copolymerized directly with phosgene.Such approaches to silicone-containing copolycarbonates are illustratedin Japanese Patent Application JP 9265663, European Patent ApplicationEP 500131, U.S. Pat. No. 5,530,083, U.S. Pat. No. 5,502,134, andcopending U.S. patent application Ser. No. 09/613,040.

Siloxane-containing bischloroformates are potentially attractivechemical intermediates for the preparation of silicone-containingmaterials, including silicone-containing copolycarbonates in which thesilicone-containing monomer is incorporated into the polymer as anelectrophilic species. As such, improved methods for the preparation ofsiloxane-containing bischloroformates represent attractive goals. Thepresent invention provides a simple, continuous, high yield method forthe preparation of high purity siloxane-containing bischloroformateswhich is superior to known methods of bischloroformate preparation.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention provides a continuous method forthe preparation of bischloroformates of siloxane bisphenols, said methodcomprising introducing into a flow reactor at least one siloxanebisphenol, at least one alkali metal hydroxide or alkaline earth metalhydroxide, and phosgene, said phosgene being introduced at a rate suchthat the ratio of phosgene to siloxane bisphenol OH groups is in a rangebetween about 2.5 and about 6 moles of phosgene per mole of siloxanebisphenol OH group, said alkali metal hydroxide or alkaline earth metalhydroxide being introduced as an aqueous solution, said aqueous solutionhaving a concentration of at least about 5 percent by weight metalhydroxide, said metal hydroxide being introduced at a rate such that themolar ratio of metal hydroxide to phosgene is in a range between about3.5 and about 6.

In another aspect, the present invention relates to the high puritysiloxane bischloroformates which may be produced by the method of thepresent invention.

BRIEF SUMMARY OF THE DRAWING

FIG. 1 illustrates a tubular reactor system suitable for use in theproduction of bischloroformates of siloxane bisphenols using the methodof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the examples included herein. In this specification and in theclaims which follow, reference will be made to a number of terms whichshall be defined to have the following meanings.

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

“BPA” is herein defined as bisphenol A and is also known as2,2-bis(4-hydroxyphenyl)propane, 4,4′-isopropylidenediphenol andp,p-BPA.

As used herein, the term “bisphenol A polycarbonate” refers to apolycarbonate in which essentially all of the repeat units comprise abisphenol A residue.

As used herein, the terms “siloxane-containing bischloroformates” andthe term “siloxane bischloroformates” are used interchangeably and referbroadly to any bischloroformate comprising one or more siloxane units.Siloxane bischloroformates comprise as a subgroup bischloroformates ofsiloxane bisphenols.

As used herein, the term “bischloroformates of siloxane bisphenols”refers to bischloroformates prepared from siloxane-containing bisphenolsor their equivalents. The disodium salt of a siloxane bisphenol is anexample of a species which would function as the equivalent of asiloxane bisphenol.

As used herein, the terms “siloxane-containing bisphenol” and “siloxanebisphenol” are interchangeable and have the same meaning. Siloxanebisphenols are dihydroxy aromatic compounds incorporating one or moresiloxane repeat units. Typically, the siloxane bisphenols used toprepare the siloxane bischloroformates are isomeric mixtures, saidisomeric mixtures arising in a double hydrosilylation reaction which istypically a synthetic step in the preparation of siloxane bisphenols.Typically, these isomeric mixtures comprise a single major isomer. Itwill be understood by those skilled in the art, however, that thestructure II given for the eugenol siloxane bisphenol used in theExamples and Comparative Examples is idealized in that it representsonly the major isomer present in an isomeric mixture. Similarly, each ofstructures III-IX represents an idealized structure meant to encompassinstances in which said structures represent only a major isomer presentin an isomeric mixture of siloxane bisphenols or siloxanebischloroformates. The description above should not be construed,however, as limiting the present invention to the use of isomericmixtures of siloxane bisphenols. The use of siloxane bisphenols whichare essentially single isomers falls well within the ambit of theinstant invention.

As used herein, the term “d-50 eugenol siloxane bisphenol” indicates aeugenol siloxane bisphenol having idealized structure II wherein theaverage value of the integer p is about 50. For convenience sake theterm “d-50 eugenol siloxane bisphenol” is abbreviated EuSiD50. Forconvenience the mixture of isomeric d-50 eugenol siloxane bisphenols IIand X used in the Examples and Comparative Examples of the instantinvention has been represented as a single structure II, the structureof the major isomer present in said mixture, wherein p has an averagevalue of about 50.

The method of the present invention relates to a method for thecontinuous preparation of bischloroformates of siloxane bisphenols. Bycontinuous, it is meant that reactants are introduced into a suitablereactor system while products are simultaneously removed from thesystem. In the present invention at least one siloxane bisphenol,phosgene, and at least one alkali metal hydroxide or alkaline earthmetal hydroxide are introduced into a flow reactor. The reactants passthrough the flow reactor forming product bischloroformate during thepassage from the point, or points, at which the reactants are introducedand the point at which an effluent stream containing product emergesfrom the reactor. It has been discovered that product yields arestrongly and unexpectedly dependent upon reaction parameters such as therelative amounts of siloxane bisphenol, metal hydroxide, and phosgene,even when a substantial excess of phosgene or metal hydroxide ispresent. Additionally, it has been found that under similar conditionsoperation of the process in a continuous mode provides unexpectedly highyields relative to analogous batch processes.

In the practice of the present invention at least one siloxanebisphenol, phosgene, and at least one alkali metal hydroxide or alkalineearth metal hydroxide are introduced into a flow reactor. The flowreactor is not particularly limited and may be any reactor system whichprovides for the “upstream” introduction of the reactants and the“downstream” removal of product bischloroformate. Suitable flow reactorsystems include tubular reactors, continuous stirred tank reactors, loopreactors, column reactors, and combinations thereof. The flow reactormay comprise a series of flow reactor components, as for example, aseries of continuous stirred tank reactors arrayed such that theeffluent from a first continuous stirred tank reactor provides the inputfor a second continuous stirred tank reactor and so forth. Combinationsof the various flow reactor components are illustrated by a first columnreactor coupled to a downstream continuous stirred tank reactor wherethe output of the column reactor represents the feed to the continuousstirred tank reactor. Additionally, the flow reactor used according tothe method of the present invention may comprise flow reactor componentsarrayed in a parallel or network fashion, for example, as where thereactants are introduced into a parallel array of two or more tubularreactors the effluent of each of which is introduced into a singlecontinuous stirred tank reactor. In one embodiment of the presentinvention the flow reactor comprises a series of tubular reactors. In analternate embodiment the flow reactor comprises a series of continuousstirred tank reactors. The reactants may be introduced into the flowreactor system through one or more feed inlets attached to the flowreactor system. Typically, it is preferred that the reactants beintroduced into the flow reactor through at least three feed inlets, forexample where a solution of the siloxane bisphenol in an organic solventsuch as methylene chloride, aqueous alkali metal hydroxide, and phosgeneare introduced through separate feed inlets at or near the upstream endof a tubular reactor. Alternative arrangements wherein one or more ofthe reactants is introduced through multiple feed inlets at variouspoints along the flow reactor are also possible. Typically, the relativeamounts of the reactants present in the flow reactor are controlled bythe rate at which they are introduced. For example, a reactant can beintroduced into the flow reactor through pumps calibrated to deliver aparticular number of moles of said reactant per unit time.

The present invention employs phosgene (COCl₂) to convert siloxanebisphenol OH groups into the corresponding chloroformate groups. It hasbeen discovered that the amount of phosgene employed strongly influencesproduct yield. Phosgene is preferably used in an amount corresponding tobetween about 2.5 and about 6, even more preferably between about 3.5and about 5.5 moles of phosgene per mole of siloxane bisphenol OH group.Expressed in terms of moles of phosgene per mole of siloxane bisphenolemployed, it is preferable to use between about 5 and about 12, and evenmore preferable between about 7 and about 11 moles of phosgene per moleof siloxane bisphenol.

The alkali metal hydroxide or alkaline earth metal hydroxide, orcombination thereof is employed as an aqueous solution used in an amountpreferably corresponding to between about 3.5 and about 6, and even morepreferably between about 4 and about 5 moles of metal hydroxide per moleof phosgene employed. The concentration of the aqueous metal hydroxidesolution employed is preferably between about 5 and about 25, and evenmore preferably between about 17 and about 25 percent by weight metalhydroxide. In one embodiment of the present invention the concentrationof the metal hydroxide solution is at least about 5 percent by weight.Of course, more concentrated solutions of metal hydroxide may be used,as long as they are supplemented with water such that the net metalhydroxide concentration in aqueous solution is about 25% by weight orless.

The siloxane bisphenol is typically introduced into the flow reactor asa solution in a solvent. Typically the solvent is methylene chloride butcan be any solvent suitable for use under interfacial reactionconditions. Typically halogenated solvents such as methylene chloride,chloroform, and 1,2-dichloroethane are preferred but othernon-halogenated solvents such as toluene or ethyl acetate may also beused. Typically the concentration of the siloxane bisphenol in thesolvent is in a range between about 5 and about 95, preferably betweenabout 10 and about 30 percent by weight siloxane bisphenol. As noted,the siloxane bisphenol employed may be a single chemical species or amixture of chemical species as is typical in siloxane bisphenols whichtypically comprise a distribution of bisphenols possessing siloxanesubunits of varying chain lengths. Alternatively, the siloxane bisphenolmay be introduced as an oil, without solvent.

In one embodiment of the present invention the siloxane bisphenolemployed comprises structure I

wherein R¹ is independently at each occurrence a C₁-C₁₀ alkylene groupoptionally substituted by one or more C₁-C₁₀ alkyl or aryl groups, anoxygen atom, an oxyalkyleneoxy moiety—O—(CH₂)_(t)—O—,or an oxyalkylene moiety—O—(CH₂)_(t)—,where t is an integer from 2-20;

-   R² and R³ are each independently at each occurrence halogen, C₁-C₆    alkoxy, C₁-C₆ alkyl, or C₆-C₁₀ aryl;-   z and q are independently integers from 0-4;-   R⁴, R⁵, R⁶ and R⁷ are each independently at each occurrence C₁-C₆    alkyl aryl, C₂-C₆ alkenyl, cyano, trifluoropropyl, or styrenyl; and-   p is an integer from 1 to about 100.

Representative examples of siloxane bisphenols I include, but are notlimited to eugenol siloxane bisphenol II and other siloxane bisphenols,for example

structures III-VII shown below in which p is an integer from 1 to about100.

The representative siloxane bisphenols; eugenol siloxane bisphenol II,4-allyl-2-methylphenol siloxane bisphenol III, 4-allylphenol siloxanebisphenol IV, 2-allylphenol siloxane bisphenol V, 4-allyloxyphenolsiloxane bisphenol VI, and 4-vinylphenol siloxane bisphenol VII arenamed after the aliphatically unsaturated phenols from which they areprepared. Thus, the name eugenol siloxane bisphenol denotes a siloxanebisphenol prepared from eugenol (4-allyl-2-methoxyphenol). Similarly thename 4-allyl-2-methylphenol siloxane bisphenol indicates the siloxanebisphenol prepared from 4-allyl-2-methylphenol. The other names givenfollow the same naming pattern.

Siloxane bisphenols may be prepared by hydrosilylation of analiphatically unsaturated phenol with a siloxane dihydride in thepresence of a platinum catalyst. This process is illustrated below foreugenol siloxane bisphenol II.

In one embodiment of the present invention employing eugenol siloxanebisphenol having structure II as a reactant, p is an integer betweenabout 20 and about 100. In an alternate embodiment eugenol siloxanebisphenol II has a value of p of about 50 said eugenol siloxanebisphenol being represented by the abbreviation EuSiD50. Those skilledin the art will understand that the values given for p in structuresI-VIII represent average values and that, for example, eugenol siloxanebisphenol having a value of p of 50 represents a mixture of siloxanebisphenol homologues having an average value of p of about 50.

Typically the reactants, siloxane bisphenol, aqueous metal hydroxide,and phosgene are introduced at one or more upstream positions along theflow reactor. As mentioned, the reactants pass through the flow reactorforming product bischloroformate during the passage from the point atwhich the reactants are introduced and the point at which an effluentstream containing product emerges from the reactor. The time requiredfor a reactant to travel from the point at which it is introduced to thepoint at which either it or a product derived from it emerges from theflow reactor is referred to as the residence time for the reactant.Typically, residence times for each reactant is in a range between about5 and about 800 seconds, preferably between about 10 and about 500seconds. Those skilled in the art will understand however that the mostpreferred residence time will depend upon the structure of the startingsiloxane bisphenol, the type of flow reactor employed and the like, andthat the most preferred residence time may be determined bystraightforward and limited experimentation.

In one embodiment the present invention provides a method for thepreparation of eugenol bischloroformate VIII

wherein p is an integer from 1 to about 100, said method comprisingintroducing into a flow reactor a eugenol siloxane bisphenol II

wherein p is an integer between 1 and about 100, as a solution inmethylene chloride comprising from about 5 to about 50 weight percenteugenol siloxane bisphenol, an aqueous solution of sodium hydroxide, andphosgene, said phosgene being introduced at a rate such that the ratioof phosgene to eugenol siloxane bisphenol OH groups is in a rangebetween about 2.5 and about 6 moles of phosgene per mole of eugenolsiloxane bisphenol OH group, said aqueous solution of sodium hydroxidehaving a concentration of at least about 5 percent by weight sodiumhydroxide, said aqueous solution of sodium hydroxide being introduced ata rate such that the molar ratio of metal hydroxide to phosgene is in arange between about 3.5 and about 6.

One embodiment of the present invention is a siloxane bischloroformateproduced by the method described herein. Thus, in one aspect the presentinvention is a siloxane bischloroformate produced by the method of thepresent invention said siloxane bischloroformate comprising structure IX

wherein R¹ is independently at each occurrence a C₁-C₁₀ alkylene groupoptionally substituted by one or more C₁-C₁₀ alkyl or aryl groups, anoxygen atom, an oxyalkyleneoxy moiety—O—(CH₂)_(t)—O—,or an oxyalkylene moiety—O——(CH₂)_(t)—,where t is an integer from 2-20;

-   R² and R³ are each independently at each occurrence, halogen, C₁-C₆    alkoxy, C₁-C₆ alkyl, or C₆-C₁₀ aryl;-   z and q are independently integers from 0-4;-   R⁴, R⁵, R⁶ and R⁷ are each independently at each occurrence C₁-C₆    alkyl, aryl, C₂-C₆ alkenyl, cyano, trifluoropropyl, or styrenyl; and-   p is an integer from 1 to about 100.

In a further embodiment, the present invention affords high puritybischloroformates having low levels of residual hydroxy endgroups. Thuswhen siloxane bisphenols having structure I are converted using themethod of the present invention to the corresponding siloxanebischloroformates having structure IX, the product bischloroformate IXcontains less than 10 percent, preferably less than 5 percent and evenmore preferably less than 1 percent residual hydroxy endgroups. The term“residual hydroxy endgroups” refers to those hydroxy groups present inthe starting siloxane bisphenol which are not converted to thecorresponding chloroformate groups in the product bischloroformate.During the course of the present invention it was discovered that theprincipal impurities present in the product siloxane bischloroformateare the starting siloxane bisphenol and bischloroformate half product asdetermined by ¹H-NMR spectroscopy. Comparative Example 1 illustrates thehigh levels of residual hydroxy endgroups present in product siloxanebischloroformate prepared using conventional batch reaction conditionswhich have been used to prepare other types of chloroformates.

In a further embodiment the present invention is a siloxanebischloroformate comprising structure VIII wherein p is an integerbetween 1 and about 100, said siloxane bischloroformate comprising fewerthan 10 percent hydroxy endgroups, said siloxane bischloroformatecomprising less than 0.5 percent carbonate groups.

EXAMPLES

The following examples are set forth to provide those of ordinary skillin the art with a detailed description of how the methods claimed hereinare carried out and evaluated, and are not intended to limit the scopeof what the inventors regard as their invention. Unless indicatedotherwise, parts are by weight and temperature is in ° C. Percentconversion of eugenol siloxane bisphenol OH groups to the correspondingchloroformate groups was determined by proton NMR spectroscopy (¹

The starting siloxane bisphenol, d-50 eugenol siloxane bisphenol(EuSiD50), used in the preparation of siloxane bischloroformates wasitself prepared by hydrosilylation of approximately two equivalents ofeugenol with approximately one equivalent of the d-50 siloxanedihydride, HSiMe₂(OSiMe₂)₅₀H, under known hydrosilylation conditions,for example those taught in copending U.S. application Ser. No.09/613,040. The product eugenol siloxane bisphenol was shown by ¹H-NMRto be a 95:5 mixture of isomeric siloxane bisphenols, said isomericsiloxane bisphenols having structures II and X respectively,

wherein p is a range of integers having an average value of about 50.

As mentioned, isomeric mixtures such as the mixture of siloxanebisphenols having structures II and X are idealized as having thestructure of the major isomer II for reasons of convenience. Thoseskilled in the art will understand that the olefin hydrosilylationchemistry employed to produce bisphenol siloxanes will almost invariablyproduce the product siloxane bisphenols as a mixture of isomers, saidmixture of isomers frequently being inseparable and yet useful inmaterials synthesis. Those skilled in the art will likewise understandthat the conversion of a mixture of isomeric siloxane bisphenols to thecorresponding bischloroformates will necessarily produce an isomericmixture of siloxane bischloroformates. As in the case of the siloxanebisphenols, the structures of said siloxane bischloroformates areidealized herein as having the structure of the major siloxanebischloroformate isomeric component. Thus, the eugenol siloxanebischloroformate prepared in the Examples and Comparative Examplesherein was an approximately 95:5 mixture of the siloxanebischloroformates corresponding to siloxane bisphenols II and X. Forconvenience in describing the practice and attributes of the instantinvention, isomeric mixtures of eugenol siloxane bischloroformates aretreated as having idealized structure VIII.

Three feed solutions, a 20 weight percent solution of d-50 eugenolsiloxane bisphenol (EuSiD50) in methylene chloride, NaOH in water, andphosgene were introduced into a tubular flow reactor in the amounts andfeed rates indicated. The tubular flow reactor employed is shown in FIG.1. Each feed solution was delivered independently to the reactor. Thed-50 eugenol siloxane bisphenol in methylene chloride (CH₂Cl₂) solutionwas pre-cooled in coil immersed in an ice water bath. The discharge endof the reactor was vented to a scrubber at atmospheric pressure. Thepressure at the feed side of the reactor was 3-5 psig. The tubular flowreactor comprised a series of KO-FLO® static mixers configured asfollows: one Type A tubular reactor section followed by six Type Btubular reactor sections. The Type A tubular reactor section comprisedsix static mixers, each of said mixers being 7 inches in length andhaving an outer diameter of ¼ of an inch. Each of the Type B tubularreactor sections comprised three static mixers; a first static mixer (11inches in length, ¼ inch outer diameter), a second static mixer (16inches in length, ⅜ inch outer diameter), and a third static mixer (16inches in length, ½ inch outer diameter). The total reactor volume wasabout 252 milliliters (mL). The initial sections of the reactor werewrapped with woven fabric insulating material. Sampling points werelocated at several locations along the flow reactor and are indicated inFIG. 1 as “Point 1”-“Point 8”, “Point 12” and “Sample Point 13”. Samplepoint 13 was located at the downstream end of the sixth Type B tubularreactor section and corresponded to a reactor volume of about 252 mL.Sample point 8 was located at the downstream edge of the first type Btubular reactor section (that tubular reactor section following the TypeA reactor section) and corresponded to a reactor volume of about 57 mL.Sample point 7 was located at the downstream end of the Type A tubularreactor section. Typical residence times are illustrated by Example 2wherein the residence time was about 90 seconds at sample point 8 andabout 400 seconds at sample point 13. In Examples 1-6 feed solutions (1)and (3) were introduced at the following rates:

-   Feed (1): 7.6 gram/minute (gm/min)EuSiD50 (d-50 eugenol siloxane)    30.4 gram/minute methylene chloride-   Feed (3): 1.12 gram/minute COCl₂

The data in Table 1 demonstrate that using the method of the presentinvention greater than 95% conversion of eugenol siloxane bisphenolhydroxy groups to the corresponding bischloroformates can be achievedwhile avoiding carbonate byproduct formation. In Examples 1-6 optimalperformance was achieved when the molar ratio of sodium hydroxide toeugenol siloxane bisphenol hydroxy groups was in a range between about 9and about 12 and the concentration of the aqueous sodium hydroxide wasabout 17.5 percent by weight sodium hydroxide in water.

TABLE 1 EUGENOL SILOXANE BISCHLOROFORMATE PREPARATION Moles Wt % NaOHFeed 2 % Conversion % Conversion Carbonate Example NaOH^(a) (Feed 2)^(b)rate^(c) at 8^(d) at 13^(e) level^(f) 1 6 17.5 5.18 82.8 <0.5% 2 9 17.57.77 94.4 95.3 <0.5% 3 12 17.5 10.36 96.3 96.5 <0.5% 4 6 12.5 5.18 72.8<0.5% 5 9 12.5 7.77 88.9 <0.5% 6 12 12.5 10.36 92.9 93.2 <0.5% ^(a)MolesNaOH per mole Eugenol siloxane bisphenol OH endgroup ^(b)Concentrationof NaOH in Feed 2 expressed as weight percent ^(c)Rate at which Feed 2was introduced expressed in grams per minute ^(d)Percent of Eugenolsiloxane bisphenol OH groups converted to bischloroformate at samplepoint 8 ^(e)Percent of Eugenol siloxane bisphenol OH groups converted tobischloroformate at sample point 13 ^(f)Level of by-product eugenolsiloxane carbonate was less than 0.5%

Comparative Example 1

A 500 mL Morton flask was charged with d-50 eugenol siloxane bisphenol(5.0 g, 0.12 mmol), methylene chloride (130 mL) and water (10 mL). ThepH was adjusted to and maintained at a pH of from about 0 to about 5with 25 wt % aqueous sodium hydroxide as phosgene (5.0 g, 50 mmol) wasadded. Following phosgene addition the pH was raised to about 10 toconsume excess phosgene. Hydrochloric acid solution (1N HCL, 135 mL) wasadded and the product bischloroformate solution was separated bycentrifugation. Proton NMR analysis showed only about 90% of the eugenolsiloxane bisphenol hydroxy groups had been converted to chloroformategroups. There was little or no carbonate coupled product.

Examples 7-24

The flow reactor used in Examples 7-24 was essentially identical to thatused in Examples 1-6 with the following modifications. The flow reactorwas configured as shown in FIG. 1. A sample port was added to the systemat the downstream end of the first reactor section (Type A tubularreactor section) and a cooler was installed to provide cooling for theaqueous caustic feed in selected experiments. Examples 17-22 utilizedthe aqueous caustic cooler. In each of Examples 7-24 the solution ofeugenol siloxane bisphenol in methylene chloride (CH₂Cl₂) was chilled inan ice water bath prior to its introduction into the flow reactorsolution cooler. Detailed Experimental conditions used in Examples 7-24are given Table 2. Additional experimental data and results for theconversion of starting eugenol siloxane bisphenol to product eugenolsiloxane bischloroformate in Examples 7-24 are gathered in Table 3. Feedrates employed in Examples 7-24 for eugenol siloxane bisphenol,methylene chloride and phosgene are given below.

Feed 1:  7.6 gram/minute EuSiD50 30.5 gram/minute CH₂Cl₂ Feed 2: COCl₂(see tables for flow rates) Feed 3: Aqueous NaOH (see tables for flowrates)

TABLE 2 EUGENOL SILOXANE BISCHLOROFORMATE REACTION CONDITIONS ResidenceNaOH Point 6 Feed Time Residence COCl2 Soln NaOH Temp Pressure Point 7Time Example gm/min gm/min ° C. ° C.^(a) psig (sec) Point 13 (sec) 71.12 10.38 15.8 43.3 5 —  804^(b) 8 1.12 12.12 13.2 38.5 2 27 379 9 1.5016.17 14.9 41.1 3 25 349 10 1.12 15.16 14.5 35.5 2.5 25 356 11 1.5020.21 16.2 40.5 4 23 323 12 1.12 9.09 12.6 38.1 3 29 410 13 1.50 12.1212.2 42.5 4.2 27 384 14 1.12 11.37 11.9 34.9 2.0 28 390 15 1.50 15.1612.9 41.5 3.8 26 361 16 1.31 11.93 12.8 40.0 3 27 383 17 1.50 15.16 8.530.5 3 26 361 18 1.69 17.05 8.8 33.1 3 25 347 19 1.87 18.94 5.8 31.4 324 335 20 1.50 12.63 6.7 34.3 3 27 383 21 1.69 14.21 6.2 36.5 3.8 26 37122 1.87 15.79 7.2 39.3 4 26 360 23 1.87 15.79 11.4 40.2 5 26 360 24 1.8717.22 14.0 43.8 4.5 26 360 ^(a)Point 6 located between the fifth andsixth static mixing elements of the Type A tubular reaction section(Labeled “Point 6” in FIG. 1) ^(b)Each Type B tubular reactor sectionwas followed by a 10 foot long ¼″ o.d. copper tube having a volume of 48mL. The total reactor volume for this example was 540 mL.

TABLE 3 EUGENOL SILOXANE BISCHLOROFORMATE PREPARATION Molar ratio COCl₂/Ex- Eugenol % Conversion to % Conversion to am- siloxane NaOH/ wt %Chloroformate Chloroformate ple OH COCl₂ ^(a) NaOH Sample Point 7 SamplePoint 13 7 3 4 17.5 — 97.7 8 3 4 15  84.7^(b) 91.3 9 4 4 15 93.0 97.1 103 5 15 85.8 91.7 11 4 5 15 97.6 98.5 12 3 4 20 88.4 96.6 13 4 4 20 98.098.5 14 3 5 20 91.3 95.7 15 4 5 20 99.0 99.0 16 3.5 4.5 17.5 97.1 97.117 4 5 20 85.5 97.6 18 4.5 5 20 87.3 98.0 19 5 5 20 88.1 99.5 20 4 5 2484.4 98.0 21 4.5 5 24 85.1 99.0 22 5 5 24 94.8 99.5 23 5 5 24 — >99.5 245 5 22 — >99.5 ^(a)mole NaOH per mole of phosgene ^(b)Sample taken atsample point No. 8 instead of sample point No. 7

The data in Table 3 demonstrate that essentially complete conversion ofeugenol siloxane bisphenol to eugenol siloxane bischloroformate isachievable using the method of the present invention. With the singleexception of Example 11 in which approximately 1 percent of the eugenolsiloxane bisphenol OH groups were converted to carbonate groups, nocarbonate was detected by proton NMR. Thus, the method of the presentinvention is clearly superior to the batch preparation of eugenolsiloxane bischloroformate illustrated by Comparative Example 1.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood by thoseskilled in the art that variations and modifications can be effectedwithin the spirit and scope of the invention.

1. A siloxane bischloroformate comprising structure IX and comprisingfewer than 10 percent hydroxy endgroups

wherein R¹ is independently at each occurrence a C₁-C₁₀ alkylene groupoptionally substituted by one or more C₁-C₁₀ alkyl or aryl groups, anoxygen atom, an oxyalkyleneoxy moiety—O—(CH₂)_(t)—O—, or an oxyalkylene moiety—O—(CH₂)_(t)—, where t is an integer from 2-20; R² and R³ are eachindependently at each occurrence, halogen, C₁-C₆ alkoxy, C₁-C₆ alkyl, orC₆-C₁₀ aryl; z and q are independently integers from 0-4; R⁴, R⁵, R⁶ andR⁷ are each independently at each occurrence C₁-C₆ alkyl, aryl, C₂-C₆alkenyl, trifluoropropyl, or styrenyl; and p is an integer from 1 toabout
 100. 2. A siloxane bischloroformate comprising structure VIII

wherein p is an integer between 1 and about 100, said siloxanebischloroformate comprising fewer than 10 percent hydroxy endgroups. 3.A siloxane bischloroformate according to claim 1 comprising fewer than 5percent hydroxy endgroups.
 4. A siloxane bischloroformate according toclaim 3 comprising fewer than 1 percent hydroxy endgroups.
 5. A siloxanebischloroformate according to claim 1 less than about 0.5 percentcarbonate groups.
 6. A siloxane bischloroformate according to claim 5comprising fewer than 5 percent hydroxy endgroups.
 7. A siloxanebischloroformate according to claim 6 comprising fewer than 1 percenthydroxy endgroups.
 8. A siloxane bischloroformate according to claim 1wherein p is an integer from 20 to about
 100. 9. A siloxanebischloroformate according to claim 1 wherein p has an average value ofabout
 50. 10. A siloxane bischloroformate according to claim 2comprising fewer than 5 percent hydroxy endgroups.
 11. A siloxanebischloroformate according to claim 10 comprising fewer than 1 percenthydroxy endgroups.
 12. A siloxane bischloroformate according to claim 2less than about 0.5 percent carbonate groups.
 13. A siloxanebischloroformate according to claim 12 comprising fewer than 5 percenthydroxy endgroups.
 14. A siloxane bischloroformate according to claim 13comprising fewer than 1 percent hydroxy endgroups.
 15. A siloxanebischloroformate according to claim 2 wherein p is an integer from 20 toabout
 100. 16. A siloxane bischloroformate according to claim 2 whereinp has an average value of about 50.